Marker expression in glioblastoma stem cells grown in vitro and after transplanation into a chick embryo xenograft brain tumor model
Date
2022
Authors
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Publisher
University of Delaware
Abstract
Glioblastoma (GBM) is the most aggressive form of brain cancer that arises in situ from transformed neural stem cells, progenitor cells, or differentiated astrocytes. It is classified as World Health Organization (WHO) grade 4 type cancer due to its highly undifferentiated nature and rapid growth rate. Because of its aggressive nature, those diagnosed with GBM have a poor prognosis and experience low survival rates. Even with advancements in treatments, patients often succumb to recurrent tumors that arise after treatment. This is theorized to be due to the common presence of cancer stem cells (CSCs) in GBM tumors. CSCs are a small population of cancer cells that can migrate from the primary tumor mass and resist radiotherapy and chemotherapy. The Galileo lab has recently isolated and classified several GBM cell lines as Glioblastoma stem cells (GSCs). These cell lines came from GBM patient specimens and were cultured using media conditions that select for stem cells. These cell lines were confirmed as GSCs by determining the presence and levels of certain well accepted stem cell markers like Nestin, Sox-2, CD133, L1CAM and ITGA6. Our lab aimed to determine if the phenotypes of the small subpopulations of GSCs differed between patient lines. My goal extended this to sort GSCs based on individual stem cell markers, determine if those sorted populations were phenotypically stable for the sorted marker and to investigate if unsorted GSCs transplanted in vivo lost stem cell marker expression (i.e., ‘differentiated”) in the brain tissue environment. Sorting experiments showed that the GSCs did not maintain their sorted protein expression level and that they had a high degree of plasticity allowing expression levels of a sorted population to change between passages. This supports the hypothesis that “stemness” is a cell state rather than a stable cell phenotype. After xenograft transplantation into chick embryo brains, GSCs that migrated from primary tumor masses and invaded either along blood vessels or diffusely did not lose their stem cell marker expression. They maintained the same marker expression profile that was expressed by them in vitro. Thus, their behavior in vivo in our xenograft model (e.g., tumor formation, invasion, etc.) reflects that of GSCs and not of “differentiated” GBM cells. These findings add to the understanding of the regulatory abilities of GSCs, how identifying them based on certain protein marker expression may be inadequate, and how they are able to invade brain tissue along blood vessels. Targeting and eradicating only a portion of the migrating stem cells will not allow for successful prevention of recurrent tumors.
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Keywords
Glioblastoma, Protein expression level, Migrating stem cells, Prevention of recurrent tumors